From: Eric Dumazet <[email protected]>
Date: Fri, 18 Oct 2019 15:20:05 -0700
> Intel test robot reported a ~7% regression on TCP_CRR tests
> that they bisected to the cited commit.
>
> Indeed, every time a new TCP socket is created or deleted,
> the atomic counter net->count is touched (via get_net(net)
> and put_net(net) calls)
>
> So cpus might have to reload a contended cache line in
> net_hash_mix(net) calls.
>
> We need to reorder 'struct net' fields to move @hash_mix
> in a read mostly cache line.
>
> We move in the first cache line fields that can be
> dirtied often.
>
> We probably will have to address in a followup patch
> the __randomize_layout that was added in linux-4.13,
> since this might break our placement choices.
>
> Fixes: 355b98553789 ("netns: provide pure entropy for net_hash_mix()")
> Signed-off-by: Eric Dumazet <[email protected]>
> Reported-by: kernel test robot <[email protected]>
Applied and queued up for -stable, thanks Eric.
